Method for heating liquid by means of steam



United States Patent 3,186,476 METHOD FOR HEATING LIQUID BY MEANS OF STEAM Yoshio Tsunoda, Setagaya-ku, Tokyo, Maomi Seko, Meguro-ku, Tokyo, Ryo Ehara, Kawasaki-sin, Shinsalru Ogawa, Nobeolra-shi, and Yasumichi Yamakoshi, Meguro-lru, Tokyo, Japan, assignors to Asahi Kasei Kogyo Kabushiki Kaisha, Kita-ku, Osaka, Japan No Drawing. Filed Apr. 14, 1961, Ser. No. 102,915

2 Claims. (Cl. 1651) The present invention relates to a method for heating liquid by means of steam-having oils added to it.

When liquid is heated by steam, the general idea is that the greater the overall coefficient of heat transfer the better. To that effect, the coefficients of heat transfer of the boundary films on both the liquid side and the steam side have to be greater. It is well known that the former coefficient will be improved as the speed of flow of the liquid to be heated within pipes increases when a multipipe type heater is used, while the latter coefiicient will depend on the extent to which adhesion of a layer of condensation to the heat transfer surface is inhibited. The use of a long pipe, vertical type heater and a forced circulation type heater remove the requirement of increase of the speed of flow of liquid within pipes. However, the requirement of inhibition of adhesion of condensation has not yet been commercially met, although placing of a thin coating of a hydrophobic material on the heat transfer surface, which causes the steam which condenses on the surface in the form of drops to drop off on forming, has been tried on an experimental scale. However, no satisfactory condensing agent for coating the steam side of the heat transfer surface has been found. There are two ways of obtaining such a coating; one is directly coating the surface with a condensing agent, and the other is by the addition of the condensing agent to the steam. The first way has been attempted by using such a substance as tetrafiuoroethylene resin solid under the name of Teflon, but difiiculties occurred because of the fact that the resin was denatured after a relatively short period of time and the denatured product was hard to remove from the heat transfer surface. It is desirable that the substance adheres to the heat transfer surface but is not readily removable from the surface or dissolved off, and that it is not easily denatured or otherwise decomposed for a long period of time under operating conditions. The second method of obtaining a coating was attempted using lard, but difficulties occurred in that decomposed products thereof accumulated on the heat transfer surface and they were difficult to remove by washing with mineral oils or detergents and they reduced the overall coefiicient of heat transfer very quickly and it was necessary to discontinue the operation. All this is required for the material used for the second way is that it has a proper water-repellencyand readily adheres to the heat transfer surface, and it does not matter whether it is easily exfoliated or dissolved. It is also desirable for the material to be chemically stable; otherwise, decomposed waste accumulates on the heat transfer surface and spoils the heat transfer.

It is an object of this invention to provide a method for heating liquid with steam.

It is another object to provide a method for heating liquid in a commercially feasible manner.

According to the present invention, a mixture of oils composed of mineral oils having -20 carbon atoms in a 3,186,476 Patented June 1, 1965 molecule and neutral saturated fatty oils is added to steam which is supplied to surfaces of pipes and at the same time liquid to be heated is forced to flow at a rate of 1-4 m. per second within the pipes.

The present condensing agent is a mixture of mineral oils having 10-20 carbon atoms per molecule and neutral saturated fatty oils. The mineral oils normally consist of hydrocarbons produced from crude oil. The saturated fatty oils include single or mixed glycerides of caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid or arachidonic acid and are neutral, preferably free from free-acids. The mineral oils are mixed with the neutral saturated fatty oils at the rate of 50-99 parts by weight of the former and l-50 parts by Weight of the latter. The mixture is added to steam at the rate of 1500 p.p.m. The mixture of oils has a strong selfcleaning activity whereby decomposed oil does not readily adhere to the heat transfer surfaces of pipes and, if it does adhere, is rapidly taken off being accompanied by condensation, with the result that the heat transfer surfaces of the pipes are always subjected to the fresh condensing agent. However, in practice, although the mixture of oils has a self-cleaning activity, the decomposed products accumulate after a long period of time until heat transfer is reduced, and it is desirable that the supply of steam be discontinued after a certain period of operation and then the heat transfer surface is washed with light mineral oils such as washing oil to remove the decomposed products. It is sufficient to wash every 30-60 days, normally. The decomposed products are so readily dispersed that they are completely removed from the pipes by dipping the pipes into the washing oil bath for about 30 min.

Enforced circulation of liquid to be heated within the pipes may be effected by any conventional means. Circulation is carried out at a rate of 1-4 m./sec.

The following Examples l-3 illustrate the defects of the conventional processes. Example 4 illustrates the present invention, but does not restrict the scope of the invention.

Example 1 An out-heating type crystallizer having 36 aluminum brass pipes of 30 mm. in outer diameter, 26.8 mm. in inner diameter and 5 m. in length, within which brine of 33 B. was passed at a rate of 3 m./sec., was operated under inner pressure of 0.5 kg./cm. while the outer surfaces of the pipes were heated with 2 kg./cm. of steam without any additives.

Example 2 Example 1 was repeated except that steam was admixed with 5 p.p.m. of #140 turbine oil. The pipes were cleaned by dipping into a light oil bath for one hour each 5 days. The operation was continued for 20 days.

Example 3 Example 1 was repeated except that steam was admixed with 5 p.p.m. of lard. The pipes were cleaned by dipping into a light oil bath for one hour each 5 days. The operation was continued for 20 days.

Example 4 Example 1 was repeated except that steam was admixed with 5 p.p.m. of a mixture of parts by weight of mineral oil (140 Redwood second) and 10 parts by weight of saturated fatty oils (glyceride of lauric acid). The pipes were cleaned by dipping into a light oil bath for 20 min. each 30 days. The operation was continued for days.

Overall coefficient of heat transfer (kcaL/mHPO.) Days Example Example Example Example First day 3, 800 6, 000 6, 000 6, 000 5th day: 7

Before cleaning 4,200 4, 300 6, 000 After cleaning 4, 500 4, 400 10th day:

Before cleaning. 3, 500 3, 700 6, 000 After cleaning..- 4, 100 4, 000 th day:

7 Before cleaning 3, 200 3, 400 6, 000 After cleaning 4, 000 3, 900 th day 3,100 3, 000 5, 800 th day:

Before cleanin 5, 500 After cleanin 6, 200 th day:

Before cleaning 5, 500 After cleanin 6,200 th day. 5, 500

What we claim is:

1. In a method for heating a liquid by indirect contact with steam, the steps of adding to said steam 1-500 ppm. of an oil mixture consisting of 50-99 parts by weight of mineral oils and 1-50 parts by weight of neutral saturated fatty oils, and flowing the liquid to be heated at a rate of 1 to 4 m./sec., whereby the overall coefiicient of transfer is greatly improved.

2. The method for heating a liquid as claimed in claim 1, wherein the saturated fatty oils are glycerides of a member selected from the group consisting of caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidonic acid, and the mineral oils consist of hydrocarbons among distillate composition of crude oil, belonging to the fraction having a boiling point in the range of ZOO-250 C. and having 10 to 20 carbon atoms in a molecule.

References Cited by the Examiner UNITED STATES PATENTS 1,995,361 3/3'5 Nagle Q. 25724 CHARLES SUKALO, Primary Examiner. HERBERT L. MARTIN, Examiner. 

1. IN A METHOD FOR HEATING A LIQUID BY INDIRECT CONTACT WITH STEAM, THE STEPS OF ADDING TO SAID STEAM 1-500 P.P.M. OF AN OIL MIXTURE CONSISTING OF 50-99 PARTS BY WEIGHT OF MINERAL OILS AND 1-50 PARTS BY WEIGHT OF NEUTRAL SATURATED FATTY OILS, AND FLOWING THE LIQUID TO BE HEATED AT A RATE OF 1 TO 4 M./SEC., WHEREBY THE OVERLL COEFFICIENT OF TRANSFER IS GREATLY IMPROVED. 